1. Field of the Invention
The present invention relates to a input/output port, and in particular to an enclosure mounted on a SMIF input/output port for allowing transfer of a bare cassette to and from a processing tool on which a SMIF input/output port is mounted, which enclosure isolates the operator from the interior of the input/output port after the cassette is loaded.
2. Description of the Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
The SMIF system provides a clean environment for articles by using a small volume of particle-free gas which is controlled with respect to motion, gas flow direction and external contaminants. Further details of one proposed system are described in the paper entitled "SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING," by Mihir Parikh and Ulrich Kaempf, Solid State Technology, Jul. 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (.mu.m) to above 200 .mu.m. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half gm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 .mu.m substantially interfere with 0.5 .mu.m geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 .mu.m and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafer cassettes; (2) a minienvironment supplied with ultraclean air flows surrounding cassette load ports and wafer processing areas of processing stations so that the environments inside the pods and minienvironment become miniature clean spaces; and (3) robotic input/output (I/O) port assemblies to load/unload wafer cassettes and/or wafers from the sealed pods to the processing equipment without contamination of the wafers in the wafer cassette from external environments. The system provides a continuous, ultraclean environment for the wafers as they move through the wafer fab.
Many wafer fabrication sites have not yet, or have only partially, transitioned to a SMIF solution. A partial transition may involve the use of the SMIF I/O port affixed to the front end of a process tool, but instead of the SMIF pods, the wafers or other such workpieces are transported around the fab in bare cassettes. In this situation, an operator carries a cassette to the I/O port and positions the cassette on a port door of the I/O port so that the cassette may thereafter be lowered down through the I/O port for workpiece transfer to and from the processing tool. Manual loading of bare cassettes onto SMIF I/O ports has conventionally presented some disadvantages.
First, when transporting bare cassettes around a fab, the workpieces within the cassette are preferably oriented at or near vertical to prevent the workpieces from falling out of the cassette. However, in order to properly load a cassette onto an I/O port, the operator must rotate the cassette so that the workpieces are horizontally oriented on the port. The repeated rotation of a cassette involved with loading and unloading cassettes to and from the various I/O ports within a fab can result in operator fatigue or repetitive strain injury to an operator's wrists and arms. Additionally, care must be taken during rotation of the cassettes to avoid vibration and rattling of the workpieces within the cassette and to prevent the workpieces from sliding forward or falling out of the cassette.
A further safety related problem is that so-called "pinch points" are created in the space between the port plate and the port door when the plate and door are separated. An operator must be careful to keep his or her hands clear of these pinch points as the port door returns to its home position seated in the port plate. A still further safety related hazard is that SMF I/O ports are typically provided with a laser underneath the port plate which is used to generate workpiece mapping and positional information. There is a concern that retinol damage may occur as a result of an operator looking into the laser when the port door is lowered away from the port plate.
In addition to safety considerations, a further concern in manual loading of bare cassettes onto a SMIF I/O port is that an operator may inadvertently damage the I/O port or the interior of the process tool to which the I/O port is affixed.